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<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        //回调地狱
        setTimeout(() => {
            console.log(1)
            setTimeout(() => {
                console.log(2)
                setTimeout(() => {
                    console.log(3)
                },1000)
            },1000)
        },2000)

        //使用Promise来消除回调地狱
        //承诺
        new Promise((resolve,reject)=>{
            setTimeout(()=>{
                resolve("2s后")
            },2000)
        }).then((msg)=>{
            console(3)
        },()=>{

        })
    </script>
</body>
</html>